Answer;
ATP.
The generation of ATP occurs by Chemiosmosis.
Explanation;
In the electron transport chain, hydrogen ions in the matrix space can only pass through the inner mitochondrial membrane through a membrane protein called ATP synthase.
As these protons move through ATP synthase, ADP is turned into ATP.
The production of ATP using the process of chemiosmosis in mitochondria is called oxidative phosphorylation.
I believe the last option is the correct one for the illustration of the single celled organism provides and the environment that it is found living in.
It does not include plant sources.